The present invention relates to a printing apparatus and, more particularly, to a portable, hand-held type printing apparatus, e.g., a printing apparatus which prints data by using an inkjet printhead.
Data to be processed by an information processor such as a personal computer is generally printed as visual information on a printing medium by using a desk-top type printing apparatus which prints the visualized information by moving the printing medium. However, with the recent spread of portable information processors such as laptop personal computers, portable printing apparatuses are highly demanded.
Such portable printing apparatuses are also required to be capable of printing data on a printing medium which is difficult to move.
To meet these demands, Japanese Patent Publication Laid-Open No. 9-248939 disclosed a printing apparatus which is manually moved on a printing medium to print data on it. FIGS. 20 and 21 show the manual printing apparatus disclosed in this Patent Publication. These drawings indicate that a printhead 53 and rollers 52 are arranged on the bottom surface of a pillar housing 51. To use this apparatus, a user holds the apparatus and pushes the rollers 52 against a printing medium 54 such as a copying sheet, thereby rotating these rollers 52 and moving the housing 51 in, e.g., a moving direction A. The apparatus outputs a printing timing signal in accordance with the rotation of the rollers 52 and causes the printhead 53 to print data in synchronism with this printing timing signal.
This manual printing apparatus uses an impact type printhead 53, which prints data in contact with the printing medium 54. To prevent degradation of the printing quality caused by changes in the contact force, the printhead 53 is supported by a spring member, and the contact force between the printhead 53 and the printing medium 54 is made stable by the elastic force of this spring member.
In the above prior art, however, the use of the impact type printhead poses the problems that large noise is generated during printing and printing can be performed only on flat printing media. Hence, the use of an inkjet printhead as a typical non-impact type printhead in place of the impact type printhead is being attempted. This inkjet printhead performs non-contact printing by discharging ink onto a printing medium. Therefore, the inkjet printhead can print data with low noise on printing media made from various materials. In addition, high printing quality can be obtained without stabilizing the contact force between a printhead and a printing medium unlike a case where the conventional impact type printhead is used.
If, however, the printhead of the arrangement shown in FIGS. 20 and 21 is simply replaced by the inkjet printhead, printing still becomes nonuniform due to a variation in the biasing force applied from the rollers 52 to the printing medium 54 when the housing is moved, a variation in the pressure being pushed by each roller 52, and a fluctuation in the moving direction A, which are caused by a shake by the hand or the like. Furthermore, when data is to be printed on a printing medium which easily expands and shrinks, such as a printing sheet placed in high-humidity environment, inferior printing readily occurs due to looseness or wrinkles of the printing medium while printing is executed by moving the housing. This problem is an extremely large burden on users who must move the printing apparatus with stable hands that do not cause the apparatus to vibrate.
The internal construction of the apparatus shown in FIGS. 20 and 21 is as follows. That is, the housing contains a moving amount detecting means which detects the moving amount of the housing by using an encoder which rotates in contact with a printing medium, and a printhead (line head) in which printing elements are arrayed in the form of a line. Since this type of portable apparatus is battery-driven, it is difficult to supply a large amount of power at one time. This makes it infeasible to simultaneously drive all printing elements (heaters) of the line head. Hence, printing is performed by time-division control by dividing the heaters of the line head into blocks. Unfortunately, this method also poses the following problems because the user manually moves the housing.
The housing moving velocity is not constant.
Since the moving velocity is not constant, the printing position shifts by the time-division control. This makes it difficult to print data over a broad region of a printing medium while constant printing quality is held. Accurate printing is sometimes impossible to perform.
Since the moving velocity is not constant, it is difficult to control printing by calculating printing timings.
Accordingly, it is an object of the present invention to provide a portable, hand-held printing apparatus capable of maintaining high printing quality even when the movement of the apparatus becomes unstable due to looseness or wrinkles of a printing medium or even when the moving velocity of the apparatus changes.
According to the present invention, the foregoing object is attained by providing a printing apparatus for printing on a printing medium by using a printhead while a user moves a housing on the printing medium, comprising: detecting means for detecting the moving velocity of the housing; supply means for supplying a driving signal for driving the printhead; holding means for holding a plurality of velocity thresholds; and adjusting means for comparing a detection result from the detecting means with the plurality of velocity threshold, and adjusting the supply timing of the driving signal on the basis of the comparing result.
It is preferable to further comprise driving means for driving a plurality of printing elements of the printhead by the driving signal, temperature detecting means for detecting the temperature of the printhead, and driving control means for controlling driving by the driving means on the basis of the temperature detected by the temperature detecting means.
In this apparatus, the driving control means preferably controls driving by time-divisionally controlling the plurality of printing elements and/or by adjusting the pulse width of the driving signal.
The apparatus preferably further comprises input means for inputting printing data from an external apparatus, e.g., input means which communicates with the external apparatus by infrared communication to input the printing data.
The apparatus desirably further comprises a roller for assisting movement of the housing.
The printhead is preferably an inkjet printhead which prints by discharging ink. This inkjet printhead preferably comprises an electrothermal transducer for generating thermal energy to be given to ink, in order to discharge the ink by using the thermal energy.
The detecting means preferably detects the moving velocity of the housing in a plurality of stages by using a plurality of velocity thresholds. The adjusting means preferably converts the moving velocity of the housing detected in the plurality of stages by the detecting means, into a control signal for adjusting the supply timing of the driving signal by using a conversion table.
In accordance with the present invention as described above, when a user moves a housing on a printing medium to print data on this printing medium by using a printhead, the moving velocity of the housing is detected. On the basis of the result of comparing the detection result with a plurality of velocity thresholds, the supply timing of a driving signal for driving the printhead is adjusted.
The invention is particularly advantageous since even when the moving velocity of the housing moved by a user changes for some reason, optimum printing corresponding to the change can be performed. Accordingly, high printing quality can be maintained.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.